Physics 152B/232 Spring 2023

Special Topic Paper: Superconducting Materials

There are a wide variety of superconducting materials, with widely different Tc's (Tc is the critical temperature, below which the material superconducts). Some materials are considered to be 'conventional', described by the BCS theory of superconductivity and its extensions; others are considered to be 'unconventional', there are many competing theories to describe unconventional superconductors but no consensus on which (if any) are right. There are also many conducting materials that are not superconducting at any attainable temperature (so Tc=0) and atmospheric pressure, some of them become superconducting under pressure.

Pick two materials that are as similar as possible to each other except that their Tc's are very different and study their similarities and differences. Try to identify the property/properties that are associated with one of the materials having much higher Tc than the other, and understand/conjecture why that may be.

For example: two metallic elements, two high Tc cuprates, two binary compounds, two layered materials, two hydrides under pressure, two organic compounds, two A15 compounds, two borides, two iron pnictides, etc.

Compare their physical properties. Show graphs and/or tables of the same property for both materials next to each other and discuss their similarities and differences.

Examples of properties in the normal state: lattice structure; resistivity, specific heat, magnetic susceptibility; Hall coefficient; thermoelectric power; magnetoresistance; density of states; compressibility; thermal expansion; photoemission spectrum; optical reflectivity; XAS; Debye temperature; melting temperature; phonon spectrum; etc.

Examples of properties in the superconducting state: critical temperature; isotope coefficient; energy gap; coherence length; London penetration depth; critical magnetic field(s); magnetization versus temperature in a magnetic field (zero field cooled and field cooled); ac magnetic susceptibility versus temperature; specific heat, London penetration depth vs temperature; Knight shift; NMR; critical current; tunneling density of states; symmetry of the order parameter.

For a list of superconducting materials you can use the reference Physica C Volume 514 (2015) that reviews a large number of superconducting materials known in 2015. Find more information on the materials from the references in those papers, other databases, by searching in Google and Web of Science, etc. Consider also superconductors discovered since 2015 such as nickelates, pressurized hydrides, twisted graphene.

Once you decide which two materials you will study send me an email with subject "152B special topic" giving that information. To avoid duplication, if those materials are the same or similar to some chosen by other students I will email you asking you to pick other ones. Check the list of materials chosen so far before emailing me.

The goal of this project is that you get to learn and understand something about those materials and what determines their Tc's, write a paper on it and make a presentation to the class, so we all get to learn about a variety of superconducting materials.

The length of the paper is up to you, I suggest between 5 and 8 pages

In addition to writing the paper, prepare a powerpoint or keynote presentation 10 minutes long to explain what you learned, which you will deliver to the class at the final exam or the last week of classes.

Start early. The sooner you decide on your materials, the better the chance that you will not have to switch them.

You should have decided your materials and emailed me with that information no later than April 27.

I would like to see an outline/draft of your paper no later than May 18, so I can give you some useful feedback.

The paper is due on June 6 (Tuesday of 10th week).
A draft or final version of your presentation (powerpoint or keynote) is due Thu June 8.


Students will present their paper either at the last lecture, Thu June 8, 3:30-4:50pm, or at the final exam, Monday June 12, 3pm-6pm.